The simple thing to do is follow the directions below. This is what I have done
and everything started working okay now for me and some of my co-workers' workstation/Laptop.
If you are using Ubuntu 11.04, 11.10, and 12.04, open command line and run the following command:
$ gksudo gedit /etc/default/halt
Now that you have your Vi or Gedit - Editor open, add this below in your file as shown
INIT_HALT = POWEROFF. Hope this helps you as it has for me.
# Default behaviour of shutdown -h / halt. Set to "halt" or "poweroff".
INIT_HALT = POWEROFF